UNIX shell

1. Write a regular expression that accepts any lines that contain at least three vowels.

   ---

   ^(.*[aeiou]){3}.*$
   

   • ^ asserts the start of the line
   • .* matches any number of characters (except newline) before the first vowel
   • [aeiou] matches a single vowel character
   • {3} specifies that the previous group (vowel) should occur at least three times
   • .* matches any remaining characters (except newline) after the third vowel
   • $ asserts the end of the line

2. Write a regular expression that accepts lines that contain the letter “a” but do not contain the letter “b”.

   ---

   ^(?!.*b).*a
   [^b]*a[^b]*
   

3. Give 4 regular expressions that specify the number of times the previous expression should appear.

   ---

   a* → 0 or more times

   a+ → 1 or more times

   a? → 0 or 1 times

   a {x,y} → between x and y times, inclusive. If x is omitted, it is 0. If y is omitted, it is infinity.

4. Write a unix shell command that display all the lines of file a.txt that contain at least a distance in kilometers(i.e. 5km)

   grep -E '\\b[0-9]+km\\b' a.txt
   

6. Write a UNIX Shell command that displays the lines in a file a.txt that contains words starting with capital letters.

   ---

   grep '^[A-Z]' a.txt > only_capital.txt
   

7. Write a UNIX command that prints all the lines from file a.txt that contains at least one binary number multiple of 4 with 5 or more digits. (ex. 010100)

   ---

   grep -E '(^|[^01]) ([01]*0{2}[01]*) ([^01]|$)' a.txt
   grep -E "([0-1]){3,}00" binar
   

8. Write a UNIX shell command that prints all unique scores of football (ex: 4-0) which appear in file a.txt. The number of goals can have at max 2 digits.

   ---

   grep -E -o '\\b[0-9]{1,2}-[0-9]{1,2}\\b' a.txt | sort -u
   cat scor | sort | uniq -u
   

9. Display lines in a file a.txt that contain at least 1 timestamp hh:mm:ss:SSS (08:04:14:893)

grep -E "\\b[0-9]{2}:[0-9]{2}:[0-9]{2}:[0-9]{3}\\b" a.txt